Export of Georeferenced 3D .obj File
This is a very specific task, if I may add a personal note to that. But luckyly I studied physics and happen to know the answer.
OBJ are saved in form of Vectors. One point is represented by 3 vectors along X,Y,Z -axis. Most likely they are called a,b,c. 0,0,0 being the origin. I don't want to go to deep into that. Unless you want that - let me now.
Representation in Form of a,b,c, in a 3D space is called a Cartesian System.
Since earth (approx) is a sphere we need to transform this Cartesian System into a Spherical System. From a,b,c, to Spherical coordinates (r, θ, φ) radial distance r, azimuthal angle θ, and polar angle φ.
you can calculate each point with this:
Cartesian (x,y,z) → Spherical (r,θ,ϕ)
r=√x2+y2+z2
θ=tan−1yx
ϕ=tan−1√x2+y2z
Last step is to calculate Sperical Coordinate to UTM which is a cylindrical projection. Which results in X and Y [Because a cylinder is a unfold rectangle]
X=rθ
y=r ln[tan(pi/4 + ϕ/2)] = r/2 ln [(1+sin(ϕ)/(1-sin(ϕ))]
There are calculators for this.
search for Cartesian to UTM / Spherical to UTM
Hope it helps